In recent years, new energy has been noticed in connection with environmental issues such as increased CO2 and depletion of resource. Among these, photovoltaic generation is considered to be hopeful. A solar battery module which would become the main stream includes a crystal type module and a thin film type module.
The crystal type solar battery module is constructed by arranging a plurality of crystallized plates (wafers) having a small area on a glass plate(a cover glass) having a size as large as the module, connecting these plates with wires, and sealing for protection these by using filler such as EVA (ethylene-vinyl acetate copolymer) and a rear surface protecting material such as Tedler (trade mark).
In the thin film type solar battery module (a substrate-integrate type solar battery module), a transparent electrode layer, a thin film semiconductor layer and a rear surface electrode are formed successively on a glass plate having a size as large as the module directly, separating each layer by a patterning technique such as laser scribing and connecting sections to obtain predetermined voltage and current. As sealing for protection, the same filler and rear surface protecting material as used for the crystal type solar battery module is used.
On the other hand, in view of the recent tendency about the setting-up of solar battery modules, there are often found that they are mounted on house roofs or are set up as a roof-integrate type solar battery module so as to provide the same function as the roof.
When the solar battery module is set up on the house roof, there are considered a problem such as “dazzle” or “glare” caused by a mirror effect at the front surface of the solar battery module at which sunlight is reflected and a problem that scenery or sky reflects on the front surface of the solar battery module to spoil the beauty of the house itself or houses around there.
In connection with such problems, the following contrivance has conventionally been made. In connection with the crystal type solar battery module, for example, use of a figured glass as the cover glass which causes irregular reflection or diffusion of light on the front surface of the cover glass has been proposed. Actually, a figured glass for exclusive use is commercialized as the cover glass usable for such purpose.
Further, in the 16th IEEE Photovoltaic Specialists Conference (minutes P. 828–p. 833) 1982, GE (General Electric Company) disclosed that such figured glass was used for a roofing type solar battery module.
On the other hand, in the thin film solar battery module, there has been studied that sub-modules having a small area are sealed with the same structure as the crystal type solar battery module to prepare the above-mentioned figured glass for exclusive use. Further, JP-A-6-45628 publication proposes that a beads-containing resin capable of diffusing light is coated on the front surface of a completed solar battery module, for example.
However, the above-mentioned method has been developed to solve the problem such as “dazzle” or “glare” caused by the reflection of sunlight on the mirror-like surface of the solar battery module and to obtain a shape of front surface having an antidazzle effect. The proposed shape is not always suited for improving the performance of the solar battery.
For example, in a case of forming a light scattering layer on a front cover glass by using an organic resin as disclosed in JP-A-6-45628 publication, there is a problem that incident light is reflected at the interface due to the difference of refractive index between the resin and the glass to cause reduction in the quantity of the incident light.
Further, there is a problem that since the reflectance of the surface of the solar battery module largely depends on an angle of incident light, a much amount of light is reflected in morning or evening because sunlight enters obliquely, whereby the output of a solar battery decreases extremely.
Further, in any information obtainable until now, there is no specific description about the shape of the front surface as in JP-A-11-330508 publication. Even though the shape of the front surface is quantified, there is no more than the indication of the roughness Ra in arithmetic average as in JP-A-11-74552, and there is no reference to the specific shape for the commercialization of products.
The present invention is to solve the above-mentioned problems and to provide a cover glass for a solar battery capable of improving the output more than by the conventional technique, and having a shape of front surface which can effectively prevent an environmental problem caused by the reflection of light at a light entering side, a method for producing the cover glass and a solar battery module using the cover glass.